Stamping black data from footage to every frame?

This is a bit tricky to explain, but I've basically got an image which I'm revealing with a piece of footage of ink as a track matte.
However, as the ink passes across the composition, the image is never fully revealed - so what I'm trying to do is take the black data from the first frame of the footage, then on the next frame it will remain while the black data from the second frame appears on top, then the third, etc etc.